Re: delphi object casting

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delphi object casting

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Join Date: Dec 2007

Location: Zagreb, Croatia

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Smola

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Re: delphi object casting

Dec 26th, 2007

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Originally Posted by adrive

i'm not sure if i'm getting this right, but i still remember java allowing me to cast an object to another type as long as their ancestors are the same?

Actually you can _cast_ any object to any class, but you cannot _assign_ an ancestor-object to a variable of its descendant class.

Therefore you cannot assign TStrings to the TStringList, only vice-versa.

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Originally Posted by adrive

I can't seem to do this in delphi, the compiler doesn't seem to understand the methods and attributes of each object even after I've casted them. What's wrong?

I cannot see a single casting in your code. Casting looks like something this:

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myQuery := TQuery( myOraQuery );

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Originally Posted by adrive

I'm trying to figure out how to stick two database query objects under the same name as illustrated :

I think TOraQuery and TADOConnection don't have the same ancestor that would have properties like ExecSQL and SQL. So you must use the approach suggested by ExplainThat.

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Originally Posted by adrive

//casting qry as a TOraQuery object :
qry := TOraQuery.Create(nil);
qry := commonObj.GetConnection('DATABASE_A');

This is not casting. This is merely creating an instance of the TOraQuery and than losing that reference immedietely afterwards (which is a memory leak).

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Originally Posted by adrive

but what i really wanted to do was to be able to use one variable to represent different types of database connection, one was TADOConnection, another TOraQuery, both sharing same qry variable.

this is because they both have some similiar method names and thus i could probably reduce my code lines by eliminating the need to do alot of conditional statements and switch between different variable types.

Unfortunately, those similar method names cannot be exploited, you'll have to duplicate your code, or use an alternative connection component.

Hope I've shed some light.

Doom on, soldier.

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Re: delphi object casting

delphi object casting

Re: delphi object casting